A typical fitting of hearing device involve hearing test, calculation of initial device settings based on the results of the hearing test, programming the device with the initial settings, fine tuning the device if necessary, and verifying the fitting with additional measurements. The current invention deals with the verification part of the fitting.
A fitting verification is necessary when the fitting outcome cannot be subjectively measured completely during the fitting session. In such a case, a fitter needs to decide how much gain should be given to a patient based on fitter's professional knowledge about the patient and the hearing device. Once the fitter sets the target gain, he needs to verify that the patient indeed receives the amount intended. The factors that affect the accuracy of the gain received by a patient include patient's ear individual anatomy, accuracy of device modeling, and device variation.
There are a couple of methods for fitting verification. One is the functional gain measurements. The other is the real ear measurements with a probe microphone. The functional gain measurement involves testing patient's hearing thresholds twice at each frequency in the sound field, first without a hearing device to get the unaided thresholds, then with the hearing device the patient is going to use to get the aided thresholds. The function gains are defined as the differences between the unaided and aided thresholds. To get a functional gain measurement, a patient needs to be sat in a booth free of reverberation. The patient's ear must be at certain distance and height in relative to the speaker from which test sounds are produced. If it is desired to test for only one ear, the non-testing ear must be masked or blocked. If these conditions are not controlled carefully, the test result may not be accurate.
The real ear measurement involves measuring sound pressure level at or near the eardrum using a probe microphone. An unaided real ear response is obtained for a patient without wearing a hearing device and an aided real ear response is obtained with the hearing devices in patient's ear. The difference between the aided and unaided real ear responses is real ear insertion gain. The factors that can affect the accuracy of a real ear measurement include the positioning of the probe microphone in relative to the eardrum, the force pinched onto the probe by the insertion of the hearing devices, and the distance and direction between the ear and the speaker from which the test sounds are produced. Acoustic reverberation of the test room/booth may also affect the test consistency. These factors make the test-retest variation of the real ear measurement relatively large. In addition, the equipment for the real ear measurement is expensive and test procedure is cumbersome. As a result, less than 30% of hearing aid dispensing professionals regularly use the method for the fitting verification.
A new method is needed for simpler and more effective fitting verification.